On a section of a highway the speed-density relationship is linear an is given by $v=\big[80 – \dfrac{2}{3}k\big]$; where $v$ is in km/h and $k$ is in veh/km. The capacity (in veh/h) of this section of the highway would be

1. $1200$
2. $2400$
3. $4800$
4. $9600$